I'm baffled that you only think you get it. AFAIK it's a feature of most roleplaying rules, though my memory may be subject to selection bias.
Perhaps you could explain it so that I can go from "thinking" I get it to knowing exactly what you are thinking and why.
The other Traveller version I'm most familiar with is CT. I don't recall it handling the "non-leathal" damage differently. At least not from the starter set rules and few other supplements I own. Am I wrong?
Speaking of other games; I can't afford to collect all the Traveller stuff let alone a bunch of different systems. Until a recent LotR game, I'd only played 2 tabletop role playing systems (I'm counting the similar versions of Traveller as one) since 1995 and only a handful before that. Mostly I was into computer games until Mongoose.
Of the computer RPG's I've played, I don't recall them differentiating between different types of damage. They even lump magic damage in with the rest and the damage just knocks down your health.
In all honesty, other than non damage attacks like stun, I'm not sure why it needs to be treated differently. A good punch in the chest could break ribs and puncture a lung requiring medical attention and a certain amount of time where you will probably not be at full capacity. A poor strike with a knife could be a wound that could be ignored until the combat ends and then just needs stitches or at high tech, a spray on antiseptic, pain killer, and sealer all in one that the person has in their own personal first aid kit and they're good to go.
I'm not criticizing you for wanting it different. I bet if you explained it well enough for me to understand I'd be more than willing to give it a try in a Traveller game you GMed.